Many aircrafts have engines supported by struts protruding from each wing. The engines are each surrounded by various structural and control components, such as a fan duct and/or a thrust reverser. To provide access to the engine for maintenance or repair, the fan duct and thrust reverser are constructed in two halves which can pivot upward about large hinge pins at the strut. Specifically, an inner acoustic wall of the fan duct may include two clam-shell portions cooperatively forming the fan duct. At facing edges of the clam-shell portions, where the two halves attach to each other and/or to the aircraft, flanges extend radially outward therefrom for attachment to the strut. A curved portion of the fan duct's inner acoustic wall, where the flanges meet with the clam-shell portions, may be referred to herein as a bifurcation panel. Each of the bifurcation panels may be welded, mechanically fastened, or otherwise fixed between the flanges and the clam-shell portions.
Bifurcation panels can be manufactured out of titanium alloys to provide temperature resistance, which allows for close proximity to the aircraft engine's core without relying on insulation blankets. Bifurcation panels may have a perforated skin configured to reduce engine noise. One type of bifurcation panel is entirely formed of b21s titanium and has welded honeycomb ribbons inside, welded between a perforated upper sheet and a solid lower sheet. Fabrication of this type of bifurcation panel is typically performed using either creep forming or hot plasticity forming with male or female die molds. The bifurcation panel is forced into the female die cavity or over the male die by means of gas pressure, while the panel is maintained at a temperature of approximately 1,550 degrees Fahrenheit. This process typically utilizes pull tabs and/or a stainless steel doubler welded around a perimeter of the bifurcation panel to its solid lower sheet. The pull tabs or doublers may form a frame with edges overlapping edges of the bifurcation panel. Furthermore, a stainless steel foil or stainless steel sheet may be required to be placed between the die and the pull tabs or doublers to prevent graphite contamination in the bifurcation panel. Unfortunately, the welds between the doubler and the solid lower sheet of the bifurcation panel often leak, which may halt the forming process due to the release of forming pressure. In addition, uneven application of forming force at discrete locations on the doubler or pull tabs may result in stresses which cause the honeycomb ribbon structure to buckle and deform to an unacceptable level.